The present invention relates to the technical field of a method and an apparatus for photoelectrically reading original images, particularly images recorded on photographic films.
At present, most of the images recorded on photographic films such as negatives and reversals (which are hereinafter referred to simply as “films”) are printed onto light-sensitive materials (photographic papers) by a technique generally called “direct exposure (analog exposure) in which the light-sensitive materials are exposed with the light protected from the films.
On the other hand, a printer which adopts a technique generally called “digital exposure”, that is, a color digital printer, has recently been commercialized. In this “color digital printer”, the image recorded on a film is read photoelectrically and converted into digital signals which are subjected to various kinds of image processing to produce recording image data; a light-sensitive material is scanned and exposed with recording light modulated in accordance with the thus produced recording image data thereby recording a (latent) image which is then made to a (finished) print.
In the color digital printer, since an image can be made to digital image data and exposure conditions used in printing can be determined by subjecting the digital image data to image data processing, a high-quality print which has not been obtained by the conventional direct exposure can be obtained by preferably executing the correction of a washed out highlight and a dull shadow due to photography with back light and an electronic flash, sharpening processing and the like. Further, a plurality of images can be composited to a single image or one image can be split into segments through the image data processing. In addition, a print can be outputted after it is optionally subjected to editing and processing in accordance with uses thereof.
Outputting the image as a print (photograph) is not the sole capability of the color digital printer; the image data can be supplied into a computer or the like and stored in recording media such as a floppy disk; hence, the image data can be put to various non-photographic uses.
The color digital printer is basically composed of: a scanner that renders reading light incident on a film and photoelectrically reads the resultant projected light with an image sensor such as a CCD line sensor thereby reading an image recorded on the film; an image processing apparatus that performs specified image processing on image data captured by the scanner or supplied from a digital camera or the like to produce image data for image recording, that is, an exposure condition; a printer (image recording apparatus) that forms a latent image on a light-sensitive material by scan exposing it with, for example, a light beam in accordance with the image data outputted from the image processing apparatus; and a processor (developing apparatus) that performs development processing on the light-sensitive material exposed by the printer to produce a (finished) print on which the image is reproduced.
It is preferable that such a color digital printer can basically process both negative-type and positive-type originals, specifically, a color negative film and a color reversal film. That is, it is preferable that the print on which the high-quality image has been reproduced can be outputted from both of the color negative and color reversal films. For attaining this, it is necessary to obtain image information which is as accurate as possible from the film as the original.
Here, a problem lies in that a big difference in color balance (light quantity balance) of the image information read by the scanner (image sensor) exists between the color negative film and the color reversal film.
In other words, a sensor system which composes the scanner (image sensor) is generally suitable for white color so that it is good for reading the color reversal film as it is. However, since a base density of the color negative film greatly differs from that of the color reversal film, a problem is created when the color negative film is read in that the color balance (light quantity balance) of image information of the color negative film read by the scanner (image sensor) greatly differs from that of the color reversal film. This problem is generated only when a so-called three-color simultaneous reading is performed and is not generated when three colors are separately read in order.
This will be described in detail below.
FIG. 5 shows an example of spectral sensitivity of a sensor system composing a scanner (image sensor). As is apparent from the figure, an image sensor for B (blue) light has sensitivity also for G (green) and R (red) light, which becomes a cause of cross talk described below.
FIG. 6 shows spectral transmittance of a base of a representative color negative film. A case in which an image formed on the base having spectral transmittance as shown in FIG. 6 is read by the scanner (image sensor) having spectral sensitivity as shown in FIG. 5 is row described herein.
In this case, the light quantity balance is adjusted among three primary colors by conventional known methods such as a method in which the storage time in each CCD sensor is changed for each color so as to align the CCD output voltages, a method in which each CCD output voltage is aligned by amplification, and the like.
Under such a condition, the above-mentioned two characteristics are combined to create spectral sensitivity characteristics as shown in FIG. 7. In such characteristics, the image sensor has a cross talk (tailing portion of long wavelength side B in FIG. 7) of spectral sensitivity; hence, a new problem which causes a remarkably muddy color is generated.
Apart from the above problem, a big difference in peak values of spectral densities (particularly in R (red color))of the color negative and color reversal films exists as shown in FIG. 9 (color negative film) and FIG. 10 (color reversal film).
Same with the case that the color balances (light quantity balance) of respective image information are different from each other, the above big difference will cause another problem that a completely different reading condition such as the light quantity balance including a light source or the like is necessary to be separately set depending on whether an image on the color reversal is read or an image on the color negative films is read.